This invention relates to an improved transducer useful in monitoring dynamic variations in the diameter of a fuel injector pipe of a diesel engine.
Recently, serious attempts have been made to diagnose diesel engine performance, and specifically, injector performance, through the use of fuel injector pipe transducers which monitor the dynamic variations in the pipe. The readings or "signatures" so obtained on an oscilloscope or other suitable recording instrument can be analysed for the purpose of determining if a malfunction exists and in some instances, localizing the particular improperly functioning component. William S. Heggie in an article published by the American Society of Mechanical Engineers, paper No. 76-DGP-3 entitled "The Use of Plastic Cold Flow in the Development of an Externally Connected Transducer for Recording Pressure-time Histories of Diesel Fuel Injection Phenomena and its Application in Fault Diagnosis" discusses certain techniques and transducer devices currently in existence. Indeed, specific transducer construction for external mounting to a fuel line has been disclosed by Heggie in U.S. Pat. No. 3,937,087 issued Feb. 10, 1976 entitled "Transducer for Engine Fuel Injection Monitoring" and U.S. Pat. No. 4,027,536 issued June 7, 1977 under the same title.
In U.S. Pat. No. 3,937,087, the transducer therein disclosed embodies a torpedo-shaped housing having an internal cavity. The diesel pipe within the cavity is in contact with a strain detector mounted on its circumference and in turn is covered by a plastic sleeve. The cavity itself is then filled with epoxy or the like with electrical leads connected to the detector and which extend therethrough to the exterior of the torpedo housing. In his more recent U.S. patent, Heggie locates the strain detector or "pressure measuring" element within the epoxy filled cavity but away from the injector pipe at a position intermediate or proximate the cavity wall above the pipe. In the latter case, the strain detector is mounted on a rubber backing connected to the cavity wall.
In these known transducers as taught by Heggie, certain disadvantages are apparent. Firstly, during the assembly of the two-sectioned transducer on the injector pipe, and due to the use of an epoxy filled cavity, care must be taken in assembling same in order not to damage the strain gauge. Indeed, in this type of construction, foil type strain gauges are preferred since they are not as susceptible to damage or improper installation during assembly of the transducer as is the case with semiconductor strain gauges. The latter type of piezo-resistive gauges are preferred due to their high coefficient of resistance change (gauge factor) and therefore higher output. Accordingly, these known transducers are not conducive to field installation by unskilled technicians and more importantly, cannot readily be removed for reinstallation without anticipated damage to the strain gauge as the gauge or gauges are effectively bonded to the epoxy enveloping the pipe.